Search PubMed⌕ Search

Biomedical subjects

A I Pack

Publications and source records attributed to A I Pack.

At least 127 records · Page 7Linked to original sources
PubMed1982

Reflex effects of aerosolized histamine on phrenic nerve activity.

Studies were conducted in anesthetized, paralyzed dogs on the effect of aerosolized histamine on phrenic nerve activity. The paralyzed dogs were ventilated in phase with their recorded phrenic nerve activity at a constant inspiratory flow-rate, using a cycle-triggered ventilator. Phrenic nerve activity was measured before and during administration of aerosolized histamine while the inspiratory flow-rate and arterial blood gases were kept constant. In addition, before and after histamine, phrenic nerve activity was recorded for single bursts during which the ventilator was switched off. The effects of histamine on respiratory resistance were prevented by prior administration of isoproterenol and atropine. Although no changes occurred in respiratory resistance, histamine increased the instantaneous magnitude of phrenic nerve activity. The effect was evident early in the inspiratory period and was found even when the lungs were not inflated. Inflation of the lungs excited phrenic nerve activity; this effect increased after histamine. All of these actions of histamine were abolished by vagotomy. We conclude that histamine increased phrenic nerve activity during inspiration by a vagal reflex.

Aerosols↗
PubMed1981

The responses of I beta cells to increases in the rate of lung inflation.

The activity of inspiratory cells in the region of the nucleus of the tractus solitarius (NTS) was recorded extracellularly in paralyzed, artificially ventilated cats either during chloralose-urethane anesthesia or following midcollicular decerebration. Twenty-three of the 68 inspiratory cells recorded in the region of the NTS were classified as I beta cells on the basis of their response to withholding lung inflation. The dynamic sensitivity of I beta cells was determined by studying their response to increases in the rate of lung inflation at constant peak volume. The I beta cells in this study showed 3 distinct patterns of response to increases in the rate of inflation. Five cells showed no change in firing pattern (fixed firing pattern). Ten cells showed an increase in the rate of rise of cell activity but no change in peak frequency (low dynamic sensitivity). Eight cells showed increases in both the rate of rise of cell activity and peak frequency (high dynamic sensitivity). It was concluded that I beta cells are not a functionally homogeneous population, at least in terms of their dynamic sensitivity. Cells showing fixed firing patterns have the characteristics of off-switch neurons. Cells with low levels of dynamic sensitivity may receive afferents from pulmonary stretch receptors. Cells showing a high degree of dynamic sensitivity may receive afferents from rapidly adapting receptors. The fact that I beta cells are not a functionally homogeneous population may explain the many divergent observations reported from studies of these cells.

Afferent Pathways↗
PubMed1981

Augmentation of phrenic neural activity by increased rates of lung inflation.

Studies were conducted in anesthetized paralyzed dogs using a cycle-triggered constant-flow ventilator, which ventilated the animal in phase with the recorded phrenic neural activity. Intermittently tests were performed in which the animal was ventilated with a different airflow for a single breath. Increased airflows, within the range generated during spontaneous breathing, caused an increased rate of rise of the moving average phrenic neurogram and a shortening of the duration of the nerve burst. The magnitude of the increase in the rate of rise of the neurogram was related to the level of inspiratory airflow. Tests with brief pulses of airflow showed that an increase in the rate of rise of the phrenic neurogram could be produced without inflating the lung above the resting tidal volume of the animal. Similar results were obtained with negative-pressure ventilation and the effects were abolished by vagotomy. This vagally mediated augmentation of phrenic neural output may accelerate the inspiratory volume change in the lung during spontaneous breathing at hyperpneic levels.

Animals↗
PubMed1981

Effects of aging on ventilatory and occlusion pressure responses to hypoxia and hypercapnia.

Studies were performed to examine the decrease in ventilatory response to hypoxia and hypercapnia in the elderly and to explore its etiology. For this purpose, matched groups of normal elderly (65 to 79 yr of age) and young subjects were used. Standard pulmonary function tests were supplemented in both groups by determination of total respiratory compliance and the ventilatory responses to hyperoxic hypercapnia and isocapnic hypoxia using rebreathing methods. While testing the ventilatory responses, we recorded minute ventilation and its components, as well as mouth occlusion pressures, and rib cage and abdominal-diaphragmatic compartmental ventilation (magnetometry). We found that ventilatory responses to both hypercapnia and hypoxia were reduced in the elderly by approximately 50%. These reductions were not related to any change in control of respiratory timing, but to a large reduction in mean inspiratory airflow. The reduced airflow could not be attributed to alterations in pulmonary mechanics since the differences in mechanics between the groups were small. Instead, since the occlusion pressure responses to hypercapnia and hypoxia were reduced in the elderly proportionately to the ventilatory responses, reduction in neuromuscular inspiratory output was likely to be the major factor.

Adult↗
PubMed1980

The mechanism of arterial hypoxia occurring in acute pancreatitis.

Respiratory Function has been measured in 14 patients with acute pancreatitis, none of whom has a previous history of cardiac or respiratory disease. Their mean age was 40 years, mean PaO2 on admission, 11 kPa, and all had normal chest radiographs at that time. Arterial hypoxia was a common development and the mean PaO2 at the time of most severe hypoxia was 8.6 kPa with the lowest individual recording 4.9 kPa. In addition to daily arterial blood gas monitoring, dynamic ventilatory tests and measurements of lung volume, transfer factor, closing volume, right to left shunts and studies of gas exchange were performed. Gas exchange and shunt measurements indicated that the major abnormality responsible for arterial hypoxia was right to left shunting. Seven patients developed radiological abnormalities, five of whom has pleural effusions. Five patients showed a mild restriction in lung volume but there were no major consistent abnormalities of dynamic ventilatory tests, transfer factor, or closing volumes. Thus small airway closure, in dependent parts of the lung and less certainly loss of surfactant are unlikely to be major factors in the aetiology of arterial hypoxia in patients with acute pancreatitis. All measurements were repeated at least three months after the acute illness. The respiratory insufficiency which occurs in this disease is possibly another variant of the adult respiratory distress syndrome.

Acute Disease↗
PubMed1978

Dyspnoea during normal pregnancy.

The incidence, severity and time-course of dyspnoea were assessed in 62 women on eight occasions throughout a normal pregnancy. Fifteen per cent of subjects noticed an increase in dyspnoea in the first trimester compared with the nonpregnant state and in almost half of them dyspnoea was experienced before 19 weeks gestation; 76% complained of this symptom by 31 weeks gestation. After this time, few subjects noticed any increase in their symptoms.

Adolescent↗
PubMed1978

Total body and exchangeable potassium in chronic airways obstruction: a controversial area?

Potassium deficiency is an important complication in the treatment of heart disease. However, there is a serious dichotomy in the literature. Severe potassium depletion has been reported in this condition when exchangeable potassium was measured whereas normal levels or marginal depletion were found in measurements of total body potassium. To clarify this situation, simultaneous measurements of total body potassium by whole-body counting, and of exchangeable potassium by isotope dilution using 43K, were made in 10 male subjects with established airways obstruction. Sequential determinations showed that exchangeable potassium increased up to 68 hours after administration, and values obtained at only 24 hours would have been a substantial underestimate. In this group of subjects neither total body nor exchangeable potassium at 48 hours was significantly different from the expected normal value.

Aged↗
PubMed1977

The effect of human pregnancy on the pulmonary transfer factor for carbon monoxide as measured by the single-breath method.

1. The pulmonary transfer factor for carbon monoxide was measured by the single-breath method in 21 pregnant women with no previous history of cardiac or respiratory disease. Measurements were made at monthly intervals throughout pregnancy and once post partum. 2. The transfer factor was higher in the first trimester of pregnancy than in the non-pregnant state. There was a fall in the transfer factor during pregnancy until 26 weeks gestation, after which no further decrease was observed. 3. The changes in transfer factor were not explained by alterations in haemoglobin concentration or alveolar volume. 4. Simultaneous serial estimation of plasma 17beta-oestradiol were performed in all the subjects. There was no obvious direct relation between changes in the concentration of this hormone and transfer factor measurements.

Adult↗
PubMed1977

Large airways function during normal pregnancy.

Specific airways conductance and forced expiratory volume in one second were measured monthly from the first trimester until term in 30 subjects in the course of a normal pregnancy. Measurements were also made in the postpartum period. There was no significant change in these measurements either throughout pregnancy or compared with postpartum values. Our results suggested that the function of the larger pulmonary airways was not altered in pregnancy.

Adolescent↗
PubMed1977

A computer system for processing data from routine pulmonary function tests.

In larger pulmonary function laboratories there is a need for computerised techniques of data processing. A flexible computer system, which is used routinely, is described. The system processes data from a relatively large range of tests. Two types of output are produced--one for laboratory purposes, and one for return to the referring physician. The system adds an automatic interpretative report for each set of results. In developing the interpretative system it has been necessary to utilise a number of arbitrary definitions. The present terminology for reporting pulmonary function tests has limitations. The computer interpretation system affords the opportunity to take account of known interaction between measurements of function and different pathological states.

Computers↗
PubMed1976

Total body potassium in cor pulmonale.

Total body potassium was measured in 12 patients with cor pulmonale, by determination of potassium-40, a naturally occurring radioisotope. In all subjects the observed value of total body potassium showed no significant depletion when compared with that predicted from height and age. All previous studies in similar groups of patients have been confined to the estimation of exchangeable potassium by the technique of isotope dilution. Results using the latter technique have shown gross potassium depletion. It is suggested that the apparent disparity between total body potassium and exchangeable potassium could be explained by the requirement for a longer equilibration period when using isotope dilution techniques in patients who are in chronic hypoxaemic state.

Aged↗